Radiation imaging apparatus and method

ABSTRACT

A plurality of radiation images of an object are acquired by iterating the steps of: beginning driving of a rotation driving unit at the time at which a breathing signal having been detected by a breathing sensor has come into a predetermined state, performing a radiation imaging operation with a set of a radiation source and a radiation detector at the time, at which the heart has come into a predetermined state, in accordance with a heartbeat signal having been detected by a heartbeat sensor within a rotation driving period, during which the rotation driving unit performs the rotation driving, and ceasing the rotation driving of the rotation driving unit at the time at which the breathing of the object has come into a state other than the predetermined state.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a radiation imaging apparatus and a radiationimaging method, wherein radiation imaging operations are performed byrotating a set of a radiation source and a radiation detector withrespect to an object.

2. Description of the Related Art

Recently, radiation imaging techniques are employed, wherein a pluralityof radiation images of an object are acquired by performing radiationimaging operations on the object from a plurality of different angles byuse of CT scanners, or the like, and wherein a three-dimensional image(volume data) is formed by reconstructing the thus acquired radiationimages. In such cases, it often occurs that a state of the object, suchas the state of the heart, varies among the plurality of the radiationimages, which have been recorded from the different angles, due toheartbeat and breathing, which are the physiological phenomena ofpersons. The variation in the state of the object adversely affectsimage quality of the three-dimensional image.

Therefore, it has heretofore been proposed to perform radiation imagingoperations in accordance with a period, with which the breathing ismade, and the heartbeat. (Reference may be made to, for example,Japanese Unexamined Patent Publication Nos. 2000-262513 and2005-021345.) Japanese Unexamined Patent Publication No. 2000-262513discloses a radiation imaging technique, wherein the radiation imagingoperations are performed a plurality of times in a manner synchronizedwith the breathing and the heartbeat, wherein the occurrence of a shiftof a pattern of the heart, or the like, among the plurality of theradiation images is thereby prevented, and wherein the radiation imagingoperations are thus performed quickly.

In cases where the period, with which the rotation of a set of an X-raytube and a radiation detector is made, is short as in the cases of theapparatuses described in Japanese Unexamined Patent Publication Nos.2000-262513 and 2005-021345, and in cases where the plurality of theradiation images per turn are detected within approximately 0.5 second,the patient need not cease the breathing forcibly, and it is possible toacquire the plurality of the radiation images at the time of the stateof the heart in a predetermined temporal phase. However, in the cases ofa cone-beam CT scanner, in which a set of a radiation source and aradiation detecting unit is rotated one turn around an object, a periodof time ranging from approximately several seconds to approximatelyseveral tens of seconds is necessary for the detection of a plurality ofradiation images. Therefore, in cases where the radiation imagingoperations are to be performed by the CT scanner so as to match with theheartbeat period and the breathing period, there is the problems in thatthe necessary number of the radiation images are not capable of beingacquired during one time of the breathing period, and in that it is notalways possible for the CT scanner, or the like, to perform theradiation imaging operations so as to match with the heartbeat periodand the breathing period.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide a radiationimaging apparatus, wherein a plurality of radiation imaging operationsin accordance with heartbeat and breathing for suppressing occurrence ofan artifact are performed efficiently. Another object of the presentinvention is to provide a radiation imaging method, wherein a pluralityof radiation imaging operations in accordance with heartbeat andbreathing for suppressing occurrence of an artifact are performedefficiently.

The present invention provides a radiation imaging apparatus,comprising:

i) a radiation source for irradiating radiation to an object,

ii) a radiation detector for detecting the radiation carrying imageinformation of the object at the time at which the radiation isirradiated from the radiation source to the object,

iii) a rotation driving unit for rotating the set of the radiationsource and the radiation detector around the object,

iv) a breathing sensor for detecting a state of breathing of the objectas a breathing signal,

v) a heartbeat sensor for detecting a state of heartbeat of the objectas a heartbeat signal,

vi) rotation control means for controlling such that the driving of therotation driving unit is begun at the time at which the breathing signalhaving been detected by the breathing sensor has come into apredetermined state, and such that the driving of the rotation drivingunit is ceased at the time at which the breathing of the object has comeinto a state other than the predetermined state, and

vii) imaging operation control means for controlling the operation ofthe set of the radiation source and the radiation detector, such that aradiation imaging operation is performed at the time, at which the hearthas come into a predetermined state, in accordance with the heartbeatsignal having been detected by the heartbeat sensor within a rotationdriving period, during which the rotation driving unit performs therotation driving by being controlled by the rotation control means.

The present invention also provides a radiation imaging method,utilizing:

i) a radiation source for irradiating radiation to an object,

ii) a radiation detector for detecting the radiation carrying imageinformation of the object at the time at which the radiation isirradiated from the radiation source to the object,

iii) a rotation driving unit for rotating the set of the radiationsource and the radiation detector around the object,

iv) a breathing sensor for detecting a state of breathing of the objectas a breathing signal, and

v) a heartbeat sensor for detecting a state of heartbeat of the objectas a heartbeat signal,

wherein a plurality of radiation images of the object are acquired byiterating the steps of:

beginning the driving of the rotation driving unit at the time at whichthe breathing signal having been detected by the breathing sensor hascome into a predetermined state,

performing a radiation imaging operation with the set of the radiationsource and the radiation detector at the time, at which the heart hascome into a predetermined state, in accordance with the heartbeat signalhaving been detected by the heartbeat sensor within a rotation drivingperiod, during which the rotation driving unit performs the rotationdriving, and

ceasing the rotation driving of the rotation driving unit at the time atwhich the breathing of the object has come into a state other than thepredetermined state.

The predetermined state of the breathing signal may be the state, inwhich the breathing is stable, and should preferably be the state, inwhich the breathing signal represents, for example, at least 95% of themaximum inspiration. Also, the predetermined state of the heart may bethe state, in which the heartbeat signal represents approximately anidentical temporal phase among the plurality of the radiation imagingoperations.

The rotation driving unit may rotate the set of the radiation source andthe radiation detector at a predetermined velocity. In such cases, theimaging operation control means may control the operation of the set ofthe radiation source and the radiation detector, such that the radiationimaging operation is performed after the set of the radiation source andthe radiation detector has been driven for rotation from the state, inwhich the set of the radiation source and the radiation detector stops,and after the velocity of the set of the radiation source and theradiation detector has thus come up to the predetermined velocity.

In cases where the radiation imaging operation is performed after thevelocity of the set of the radiation source and the radiation detectorhas come up to the predetermined velocity, the rotation control meansmay have a function for returning the position of the set of theradiation source and the radiation detector in the direction, which isreverse to the direction of the rotation of the set of the radiationsource and the radiation detector at the time of the radiation imagingoperation, after a radiation imaging operation performed most recentlyhas been completed or before a next radiation imaging operation isbegun, such that the rotation driving of the set of the radiation sourceand the radiation detector is begun at the predetermined velocity from apredetermined position. Particularly, in such cases, the rotationcontrol means may have the function for returning the position of theset of the radiation source and the radiation detector, such that therotation driving of the set of the radiation source and the radiationdetector is begun at the predetermined velocity from the position, atwhich the rotation driving of the rotation driving unit has been ceasedat the stage of the radiation imaging operation performed most recently.

Alternatively, the imaging operation control means may control such thatthe radiation imaging operation is performed at the time, at which theset of the radiation source and the radiation detector takes apredetermined angular position, during the period between the state, inwhich the set of the radiation source and the radiation detector stops,and the stage, at which the velocity of the set of the radiation sourceand the radiation detector comes up to the predetermined velocity.

As another alternative, the rotation control means may control therotation driving unit such that the set of the radiation source and theradiation detector is rotated a plurality of turns. In such cases, theimaging operation control means may control the operation of the set ofthe radiation source and the radiation detector, such that the radiationimaging operation is performed with respect to an angular position takenby the set of the radiation source and the radiation detector during theperiod between the state, in which the set of the radiation source andthe radiation detector stops at the time of a predetermined turn, andthe stage, at which the velocity of the set of the radiation source andthe radiation detector comes up to the predetermined velocity at thetime of the predetermined turn, the radiation imaging operation withrespect to the angular position being performed at the time of the nextturn. The set of the radiation source and the radiation detector may berotated the plurality of turns in a predetermined direction.Alternatively, the set of the radiation source and the radiationdetector may be rotated the plurality of turns by being rotated in thepredetermined direction and in the reverse direction.

Also, the radiation imaging operation may be performed with thepredetermined imaging operation timing described above under thecondition in which the set of the radiation source and the radiationdetector is being rotated. Alternatively, the rotation control means maycontrol such that the rotation driving of the set of the radiationsource and the radiation detector by the rotation driving unit is ceasedat the time of the radiation imaging operation, and such that therotation driving is again begun after the radiation imaging operationhas been performed.

Further, the imaging operation control means may control the operationof the set of the radiation source and the radiation detector, such thatthe radiation imaging operation is performed at the time, at which aheartbeat signal component representing that the heart has come into thepredetermined state has been detected by the heartbeat sensor, withinthe rotation driving period, during which the rotation driving unitperforms the rotation driving by being controlled by the rotationcontrol means.

With the radiation imaging apparatus and the radiation imaging method inaccordance with the present invention, the plurality of the radiationimages of the object are acquired by iterating the steps of:

beginning the driving of the rotation driving unit at the time at whichthe breathing signal having been detected by the breathing sensor hascome into the predetermined state,

performing the radiation imaging operation with the set of the radiationsource and the radiation detector at the time, at which the heart hascome into the predetermined state, in accordance with the heartbeatsignal having been detected by the heartbeat sensor within the rotationdriving period, during which the rotation driving unit performs therotation driving, and

ceasing the rotation driving of the rotation driving unit at the time atwhich the breathing of the object has come into a state other than thepredetermined state.

Thus, with the radiation imaging apparatus and the radiation imagingmethod in accordance with the present invention, in cases where the setof the radiation source and the radiation detector is rotated around theobject and performs the radiation imaging operations in accordance withthe breathing and the heartbeat of the object, the rotation driving isceased with respect to the period, during which the breathing and theimaging operation timing do not match with each other, and during whichthe radiation imaging operation is not capable of being performed. Thusthe problems are prevented from occurring in that the rotation drivingalone is performed without the set of the radiation source and theradiation detector performing the radiation imaging operation.Therefore, the plurality of the radiation images are acquiredefficiently, such that the adverse effects of variation in state of theobject due to the breathing and the heartbeat of the object aresuppressed to the minimum.

The radiation imaging apparatus in accordance with the present inventionmay be modified such that the rotation driving unit rotates the set ofthe radiation source and the radiation detector at the predeterminedvelocity, and

the imaging operation control means controls the operation of the set ofthe radiation source and the radiation detector, such that the radiationimaging operation is performed after the set of the radiation source andthe radiation detector has been driven for rotation from the state, inwhich the set of the radiation source and the radiation detector stops,and after the velocity of the set of the radiation source and theradiation detector has thus come up to the predetermined velocity.

At the time at which the rotation of the set of the radiation source andthe radiation detector is begun, a certain length of time is requireddue to inertia force before the velocity of the set of the radiationsource and the radiation detector comes up to the predeterminedvelocity. With the modification described above, wherein the imagingoperation control means controls the operation of the set of theradiation source and the radiation detector, such that the radiationimaging operation is begun after the velocity of the set of theradiation source and the radiation detector has come up to thepredetermined velocity, a difference in imaging operation conditionsamong the plurality of the radiation imaging operations is suppressed tothe minimum, and image quality of the three-dimensional imagereconstructed from the plurality of the radiation images is preventedfrom becoming bad.

Also, the radiation imaging apparatus in accordance with the presentinvention may be modified such that the rotation control means has thefunction for returning the position of the set of the radiation sourceand the radiation detector in the direction, which is reverse to thedirection of the rotation of the set of the radiation source and theradiation detector at the time of the radiation imaging operation, afterthe radiation imaging operation performed most recently has beencompleted or before the next radiation imaging operation is begun, suchthat the rotation driving of the set of the radiation source and theradiation detector is begun at the predetermined velocity from thepredetermined position. Particularly, in such cases, the radiationimaging apparatus in accordance with the present invention may bemodified such that the rotation control means has the function forreturning the position of the set of the radiation source and theradiation detector, such that the rotation driving of the set of theradiation source and the radiation detector is begun at thepredetermined velocity from the position, at which the rotation drivingof the rotation driving unit has been ceased at the stage of theradiation imaging operation performed most recently. With themodification described above, the problems are prevented from occurringin that a position, at which the radiation imaging operation is notperformed, arises with respect to the period between the stage, at whichthe rotation of the set of the radiation source and the radiationdetector is begun, and the stage, at which the velocity of the set ofthe radiation source and the radiation detector comes up to thepredetermined velocity.

Further, the radiation imaging apparatus in accordance with the presentinvention may be modified such that the imaging operation control meanscontrols such that the radiation imaging operation is performed at thetime, at which the set of the radiation source and the radiationdetector takes the predetermined angular position, during the periodbetween the state, in which the set of the radiation source and theradiation detector stops, and the stage, at which the velocity of theset of the radiation source and the radiation detector comes up to thepredetermined velocity. With the modification described above, theproblems are prevented from occurring in that a position, at which theradiation imaging operation is not performed, arises with respect to theperiod between the stage, at which the rotation of the set of theradiation source and the radiation detector is begun, and the stage, atwhich the velocity of the set of the radiation source and the radiationdetector comes up to the predetermined velocity.

Furthermore, the radiation imaging apparatus in accordance with thepresent invention may be modified such that the rotation control meanscontrols the rotation driving unit such that the set of the radiationsource and the radiation detector is rotated the plurality of turns, and

the imaging operation control means controls the operation of the set ofthe radiation source and the radiation detector, such that the radiationimaging operation is performed with respect to the angular positiontaken by the set of the radiation source and the radiation detectorduring the period between the state, in which the set of the radiationsource and the radiation detector stops at the time of the predeterminedturn, and the stage, at which the velocity of the set of the radiationsource and the radiation detector comes up to the predetermined velocityat the time of the predetermined turn, the radiation imaging operationwith respect to the angular position being performed at the time of thenext turn.

With the modification described above, the problems are prevented fromoccurring in that a position, at which the radiation imaging operationis not performed, arises with respect to the period between the stage,at which the rotation of the set of the radiation source and theradiation detector is begun, and the stage, at which the velocity of theset of the radiation source and the radiation detector comes up to thepredetermined velocity.

Also, the radiation imaging apparatus in accordance with the presentinvention may be modified such that the rotation control means beginsthe driving of the rotation driving unit at the time, at which thebreathing signal represents at least 95% of the maximum inspiration, andsuch that the rotation control means ceases the driving of the rotationdriving unit at the time, at which the breathing signal represents alevel lower than 95% of the maximum inspiration. With the modificationdescribed above, lowering of the image quality due to up and downbreathing movement is suppressed to the minimum.

Further, the radiation imaging apparatus in accordance with the presentinvention may be modified such that the rotation control means controlssuch that the rotation driving of the set of the radiation source andthe radiation detector by the rotation driving unit is ceased at thetime of the radiation imaging operation, and such that the rotationdriving is again begun after the radiation imaging operation has beenperformed. With the modification described above, the lowering of theimage quality due to the motion artifact caused to occur by the rotationis prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an embodiment of the radiationimaging apparatus in accordance with the present invention,

FIG. 2 is a side view showing the embodiment of FIG. 1,

FIG. 3 is a block diagram showing the embodiment of FIG. 1,

FIG. 4 is a graph showing an example of a heartbeat signal detected by aheartbeat sensor in the embodiment of FIG. 1 and an example of abreathing signal detected by a breathing sensor in the embodiment ofFIG. 1,

FIG. 5 is a graph showing an example of a state, in which driving of arotation driving unit is performed or ceased by rotation control meansshown in FIG. 3,

FIG. 6 is a graph showing a different example of a state, in which thedriving of the rotation driving unit is performed or ceased by therotation control means shown in FIG. 3,

FIG. 7 is an explanatory diagram showing a different example of a state,in which the driving of the rotation driving unit is performed or ceasedby the rotation control means shown in FIG. 3,

FIG. 8 is a graph showing a different example of a state, in which thedriving of the rotation driving unit is performed or ceased by therotation control means shown in FIG. 3, and

FIG. 9 is a flow chart showing an embodiment of the radiation imagingmethod in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will hereinbelow be described in further detailwith reference to the accompanying drawings.

FIG. 1 is a perspective view showing an embodiment of the radiationimaging apparatus in accordance with the present invention. FIG. 2 is aside view showing the embodiment of FIG. 1. FIG. 3 is a block diagramshowing the embodiment of FIG. 1. A radiation imaging apparatus 1 is acone-beam CT scanner for performing imaging operations on an object fromvarious different directions and thereby acquiring a plurality ofradiation images to be used for the formation of a three-dimensionalimage. The radiation imaging apparatus 1 comprises a radiation source 2,a radiation detector 3, a C-arm 4, and a rotation driving unit. Theradiation source 2 irradiates radiation toward an object S lying on abed 6. The radiation detector 3 detects the radiation carrying imageinformation of the object S as a radiation image at the time at whichthe radiation is irradiated from the radiation source 2 toward theobject S.

The radiation source 2 and the radiation detector 3 are secured toopposite ends of the C-arm 4 so as to stand facing each other. The C-arm4 is located on a support base 5 such that the C-arm 4 is capable ofbeing moved by a rotation driving unit 30 in a direction indicated bythe arrow θ and in a direction indicated by the arrow Z. Therefore, bythe rotation of the C-arm 4, the set of the radiation source 2 and theradiation detector 3 is rotated around the object S for performing theradiation imaging operations. The rotation driving unit 30 rotates theset of the radiation source 2 and the radiation detector 3 at a velocitysuch that, for example, a period of time ranging from approximatelyseveral seconds to approximately several tens of seconds is required perturn.

A heartbeat sensor 31 is an electrocardiograph for detecting the stateof the heartbeat of the object S as a heartbeat signal HS. The heartbeatsensor 31 has a structure capable of being releasably fitted to theobject S. The heartbeat signal HS is outputted from the heartbeat sensor31 as the signal having a predetermined heartbeat period as illustratedin FIG. 4. Also, a breathing sensor 32 detects the state of thebreathing of the object S as a breathing signal BS. The breathing sensor32 has a structure capable of being releasably fitted to the object S.The breathing signal BS is outputted as a signal as illustrated in FIG.4, which has a large signal value at the time of the inspiration, andwhich has a small signal value at the time of the expiration.

Rotation control means 40 illustrated in FIG. 3 controls the operationof the rotation driving unit 30 and thereby controls the position forthe imaging operation performed by the set of the radiation source 2 andthe radiation detector 3. In this embodiment, the rotation control means40 controls the rotation driving unit 30, such that the rotation drivingis begun at the time, at which the breathing signal BS having beendetected by the breathing sensor 32 has come into a predetermined state.Specifically, the rotation control means 40 controls such that theoperation of the rotation driving unit 30 is begun at the time, at whichthe breathing signal BS having been detected by the breathing sensor 32represents at least 95% of the maximum breathing signal, and such thatthe driving of the rotation driving unit 30 is ceased at the time, atwhich the breathing signal BS represents a level lower than 95% of themaximum breathing signal.

Imaging operation control means 50 controls the radiation imagingoperations performed by the set of the radiation source 2 and theradiation detector 3. In this embodiment, the imaging operation controlmeans 50 controls such that the radiation imaging operations areperformed at the time of a rotation driving period RP, during which therotation driving unit 30 performs the rotation driving by beingcontrolled by the rotation control means 40, and such that the radiationimaging operations are not performed at the time, at which the drivingof the rotation driving unit 30 is being ceased. Also, the imagingoperation control means 50 controls the operation of the set of theradiation source 2 and the radiation detector 3, such that the radiationimaging operation is performed at the time, at which the heart has comeinto a predetermined state, in accordance with the heartbeat signal HShaving been detected by the heartbeat sensor 31. For example, theimaging operation control means 50 controls the operation of the set ofthe radiation source 2 and the radiation detector 3 such that, of a Pwave, a Q wave, an R wave, an S wave, and a T wave, which are containedin the heartbeat signal HS having been detected by the heartbeat sensor31, the timing synchronized with the R wave is taken as an imagingoperation timing ST.

As described above, the driving and the ceasing of the rotation of theset of the radiation source 2 and the radiation detector 3, and theradiation imaging operations are controlled in accordance with thebreathing signal BS and the heartbeat signal HS. In this manner, aplurality of the radiation images are acquired efficiently, such thatthe adverse effects of variation in state of the object due to thebreathing and the heartbeat of the object S are suppressed to theminimum. Specifically, since the breathing is capable of beingcontrolled artificially to a certain extent, in cases where ordinaryradiation imaging operations are performed, the radiation imagingoperations may be performed, while the breath is being stopped for alength of time of, for example, several seconds, and the adverse effectsof the up and down movement due to the breathing are thereby capable ofbeing suppressed. However, in the cases of the radiation imagingoperations with the aforesaid cone-beam CT scanner, or the like, sincean image operation time ranging from approximately several seconds toapproximately several tens of seconds is required, it is not alwayspossible to stop the breath until the radiation imaging operations arecompleted. In such cases, the radiation imaging operations for acquiringa necessary number of radiation images are performed over a plurality oftimes of breathing. However, if the imaging operations are merelyperformed only in the cases synchronized with the breathing and theheartbeat, while the set of the radiation source 2 and the radiationdetector 3 are being rotated, many positions, at which the radiationimaging operations are not capable of being performed, will arise, andtherefore the efficient radiation imaging operations will not be capableof being performed.

Therefore, in this embodiment, the rotation driving and the radiationimaging operations are turned on and off in accordance with thebreathing and the heartbeat of the object S, and the plurality of theradiation images, in which the variation due to the up and down movementamong the radiation images has been suppressed to the minimum, arethereby acquired efficiently without an excessive burden being imposedupon the object S. Accordingly, a three-dimensional reconstructed imageis formed with a high accuracy such that a motion artifact issuppressed.

In the embodiment described above, the imaging operation control means50 controls such that the radiation imaging operation is performed fromthe stage immediately after the driving of the rotation driving unit 30has been begun. Alternatively, the radiation imaging operation may bebegun after the driving of the rotation driving unit 30 has been begunand after the velocity of the set of the radiation source 2 and theradiation detector 3 has thus come up to a predetermined velocity. FIG.5 is a graph showing an example of a state, in which the driving of therotation driving unit 30 is performed or ceased by the rotation controlmeans 40 shown in FIG. 3. Specifically, as illustrated in FIG. 5, therotation driving unit 30 does not enable the set of the radiation source2 and the radiation detector 3 to rotate at the predetermined velocityimmediately after the rotation driving has been begun, but a preparatoryperiod PP is required before the velocity of the set of the radiationsource 2 and the radiation detector 3 come up to the predeterminedvelocity. In cases where the radiation imaging operation is begun afterthe velocity of the set of the radiation source 2 and the radiationdetector 3 has come up to the predetermined velocity, the plurality ofthe radiation images are acquired under identical imaging operationconditions.

In cases where the preparatory period PP is short and is thusnegligible, the radiation imaging operation may be performed only in thestate, in which the velocity of the set of the radiation source 2 andthe radiation detector 3 has come up to the predetermined velocity.However, it may often occur that a certain length of time is required asthe preparatory period PP, and it is therefore desired to perform theradiation imaging operation also with respect to the preparatory periodPP. In such cases, the imaging operation control means 50 may controlsuch that the radiation imaging operation is performed with a timingsynchronized with the heartbeat at the time, at which the set of theradiation source 2 and the radiation detector 3 takes a predeterminedposition for the radiation imaging operation (a predetermined rotationangle), within the preparatory period PP before the velocity of the setof the radiation source 2 and the radiation detector 3 comes up to thepredetermined velocity.

FIG. 6 is a graph showing a different example of a state, in which thedriving of the rotation driving unit 30 is performed or ceased by therotation control means 40 shown in FIG. 3. Also, FIG. 7 is anexplanatory diagram showing a different example of a state, in which thedriving of the rotation driving unit 30 is performed or ceased by therotation control means 40 shown in FIG. 3. As another alternative, asillustrated in FIG. 6 and FIG. 7, the rotation control means 40 maydrive the rotation driving unit 30, such that the position of the set ofthe radiation source 2 and the radiation detector 3 is returned to theposition, which is taken at the time of the completion of the period ofthe imaging operation performed most recently, after the rotationdriving period RP for the rotation driving performed most recently hasbeen completed or before the next rotation driving period RP is begun.Specifically, the rotation driving unit 30 is rotated in the reversedirection by the angle corresponding to the rotation, which is performedduring the preparatory period PP at the time of the initial movement ofthe rotation driving unit 30, and the rotation, which is performedduring the preparatory period PP at the time of the final movement ofthe rotation driving unit 30, and the position of the set of theradiation source 2 and the radiation detector 3 is thereby returned. Asa result, when the next radiation imaging operation is performed, thenext radiation imaging operation is begun in the state, in which the setof the radiation source 2 and the radiation detector 3 is rotated at thepredetermined velocity, from the position, at which the radiationimaging operation performed most recently has been completed (i.e., fromthe position, at which the rotation at the predetermined velocity hasbeen completed at the stage of the radiation imaging operation performedmost recently). Therefore, the problems are prevented from occurring inthat a lack of a radiation image arises since the radiation imagingoperation is not performed within the preparatory period PP.

As a further alternative, in lieu of the position of the set of theradiation source 2 and the radiation detector 3 being returned at eachof the stages, at which the operation of the rotation driving unit 30 isceased, the set of the radiation source 2 and the radiation detector 3may be rotated one turn, during which the radiation imaging operationsare performed only in cases where the velocity of the set of theradiation source 2 and the radiation detector 3 has come up to thepredetermined velocity. Thereafter, the rotation driving unit 30 may berotated in the direction, which is identical with the direction ofrotation performed one turn as described above, or in the reversedirection, and the radiation imaging operation may then be performedwith respect to the position for the radiation imaging operation withinthe preparatory period PP. FIG. 8 is a graph showing a different exampleof a state, in which the driving of the rotation driving unit 30 isperformed or ceased by the rotation control means 40 shown in FIG. 3.Specifically, as illustrated in FIG. 7 and FIG. 8, the imaging operationcontrol means 50 controls such that the radiation imaging operation isbegun after the driving of the rotation driving unit 30 has been begunand after the velocity of the set of the radiation source 2 and theradiation detector 3 has thus come up to the predetermined velocity.Also, the rotation control means 40 controls such that the set of theradiation source 2 and the radiation detector 3 is rotated one turn.Thereafter, the rotation control means 40 controls the rotation drivingunit 30 such that the set of the radiation source 2 and the radiationdetector 3 is rotated in the forward direction or in the reversedirection in order for the radiation imaging operation to be performedwith respect to the position corresponding to the preparatory period PP.In such cases, the position for the imaging operation, which positioncorresponds to the preparatory period PP, has been detected at the timeof the rotation driving performed most recently, and the imagingoperation control means 50 controls such that the radiation imagingoperation in accordance with the breathing and the heartbeat isperformed with respect to the thus detected position for the imagingoperation. In such cases, the problems are prevented from occurring inthat a lack of a radiation image arises since the radiation imagingoperation is not performed within the preparatory period PP.

FIG. 9 is a flow chart showing an embodiment of the radiation imagingmethod in accordance with the present invention. The embodiment of theradiation imaging method in accordance with the present invention willhereinbelow be described with reference to FIG. 1 through FIG. 9.Firstly, in the state in which the object S lies on the bed 6, theheartbeat sensor 31 and the breathing sensor 32 are fitted to the objectS. Thereafter, in a step ST1, the set of the radiation source 2 and theradiation detector 3 is located at the initial position. Also, in a stepST2, the detection of the heartbeat signal HS by the heartbeat sensor 31and the detection of the breathing signal BS by the breathing sensor 32are begun.

Thereafter, in a step ST3, a judgment is made by the rotation controlmeans 40 as to whether the breathing signal BS has or has not come intothe predetermined state (in which the breathing signal BS represents atleast 95% of the maximum inspiration). (Reference may be made to FIG.4.) In a step ST4, in cases where it has been judged that the breathingsignal BS has come into the predetermined state, the driving of therotation driving unit 30 is begun, and the set of the radiation source 2and the radiation detector 3 is rotated around the object S. At thistime, in a step ST5 and through a step ST6, the imaging operationcontrol means 50 takes a predetermined temporal phase of the heartbeatsignal HS as each of imaging operation timings ST, ST, . . . . Therotation of the set of the radiation source 2 and the radiation detector3 and a plurality of the radiation imaging operations are performed withthe imaging operation timings ST, ST, . . . . (Reference may be made toFIG. 4 and FIG. 5.)

In cases where it has been judged by the rotation control means 40 inthe step ST6 that the breathing signal BS has come into a state otherthan the predetermined state (in which the breathing signal BSrepresents at least 95% of the maximum inspiration), in a step ST7, therotation driving of the set of the radiation source 2 and the radiationdetector 3 by the rotation driving unit 30 is ceased, and the radiationimaging operation is ceased. (Reference may be made to FIG. 5.)Thereafter, the judgment is made by the rotation control means 40 as towhether the breathing signal BS has or has not come into thepredetermined state (in which the breathing signal BS represents atleast 95% of the maximum inspiration). Also, in cases where it has beenjudged that the breathing signal BS has come into the predeterminedstate, the radiation imaging operations are performed. In the step ST3through the step ST7, the aforesaid operations for making the judgmentand for performing the radiation imaging operations are iterated. Insuch cases, as illustrated in FIG. 6 and FIG. 7, after the driving ofthe rotation driving unit 30 has been ceased, the position of the set ofthe radiation source 2 and the radiation detector 3 may be returned byan angle corresponding to the preparatory period PP. Alternatively, asillustrated in FIG. 7 and FIG. 8, after one turn of the set of theradiation source 2 and the radiation detector 3 has been completed, theset of the radiation source 2 and the radiation detector 3 may berotated in the forward direction or in the reverse direction, and theradiation imaging operation may then be performed with respect to theposition for the imaging operation, which position corresponds to thepreparatory period PP.

With the embodiment described above, the plurality of the radiationimages of the object S are acquired by iterating the steps of:

beginning the driving of the rotation driving unit 30 at the time atwhich the breathing signal BS having been detected by the breathingsensor 32 has come into the predetermined state,

performing the radiation imaging operation with the set of the radiationsource 2 and the radiation detector 3 at the time, at which the hearthas come into the predetermined state, in accordance with the heartbeatsignal HS having been detected by the heartbeat sensor 31 within therotation driving period, during which the rotation driving unit 30performs the rotation driving, and

ceasing the rotation driving of the rotation driving unit 30 at the timeat which the breathing of the object S has come into a state other thanthe predetermined state.

Thus, with the embodiment described above, in cases where the set of theradiation source 2 and the radiation detector 3 is rotated around theobject S and performs the radiation imaging operations in accordancewith the breathing and the heartbeat of the object S, the rotationdriving is ceased with respect to the period, during which the breathingand the imaging operation timing do not match with each other, andduring which the radiation imaging operation is not capable of beingperformed. Thus the problems are prevented from occurring in that therotation driving alone is performed without the set of the radiationsource 2 and the radiation detector 3 performing the radiation imagingoperation. Therefore, the plurality of the radiation images are acquiredefficiently, such that the adverse effects of the variation in state ofthe object S due to the breathing and the heartbeat of the object S aresuppressed to the minimum.

As illustrated in FIG. 5, the radiation imaging apparatus 1 inaccordance with the present invention may be modified such that therotation driving unit 30 rotates the set of the radiation source 2 andthe radiation detector 3 at the predetermined velocity, and

the imaging operation control means 50 controls the operation of the setof the radiation source 2 and the radiation detector 3, such that theradiation imaging operation is performed after the set of the radiationsource 2 and the radiation detector 3 has been driven for rotation fromthe state, in which the set of the radiation source 2 and the radiationdetector 3 stops, and after the velocity of the set of the radiationsource 2 and the radiation detector 3 has thus come up to thepredetermined velocity.

At the time at which the rotation of the set of the radiation source 2and the radiation detector 3 is begun, a certain length of time isrequired due to inertia force before the velocity of the set of theradiation source 2 and the radiation detector 3 comes up to thepredetermined velocity. With the modification described above, whereinthe imaging operation control means 50 controls the operation of the setof the radiation source 2 and the radiation detector 3, such that theradiation imaging operation is begun after the velocity of the set ofthe radiation source 2 and the radiation detector 3 has come up to thepredetermined velocity, a difference in imaging operation conditionsamong the plurality of the radiation imaging operations is suppressed tothe minimum, and the image quality of the three-dimensional imagereconstructed from the plurality of the radiation images is preventedfrom becoming bad.

Also, as illustrated in FIG. 6 and FIG. 7, the radiation imagingapparatus 1 in accordance with the present invention may be modifiedsuch that the rotation control means 40 has the function for returningthe position of the set of the radiation source 2 and the radiationdetector 3 in the direction, which is reverse to the direction of therotation of the set of the radiation source 2 and the radiation detector3 at the time of the radiation imaging operation, after the radiationimaging operation performed most recently has been completed or beforethe next radiation imaging operation is begun, such that the rotationdriving of the set of the radiation source 2 and the radiation detector3 is begun at the predetermined velocity from the position, at which therotation driving of the rotation driving unit 30 has been ceased at thestage of the radiation imaging operation performed most recently. Withthe modification described above, the problems are prevented fromoccurring in that a position, at which the radiation imaging operationis not performed, arises with respect to the period between the stage,at which the rotation of the set of the radiation source 2 and theradiation detector 3 is begun, and the stage, at which the velocity ofthe set of the radiation source 2 and the radiation detector 3 comes upto the predetermined velocity.

Further, the radiation imaging apparatus 1 in accordance with thepresent invention may be modified such that the imaging operationcontrol means 50 controls such that the radiation imaging operation isperformed at the time, at which the set of the radiation source 2 andthe radiation detector 3 takes the predetermined angular position,during the period between the state, in which the set of the radiationsource 2 and the radiation detector 3 stops, and the stage, at which thevelocity of the set of the radiation source 2 and the radiation detector3 comes up to the predetermined velocity. With the modificationdescribed above, the problems are prevented from occurring in that aposition, at which the radiation imaging operation is not performed,arises with respect to the period between the stage, at which therotation of the set of the radiation source 2 and the radiation detector3 is begun, and the stage, at which the velocity of the set of theradiation source 2 and the radiation detector 3 comes up to thepredetermined velocity.

Furthermore, as illustrated in FIG. 7 and FIG. 8, the radiation imagingapparatus 1 in accordance with the present invention may be modifiedsuch that the rotation control means 40 controls the rotation drivingunit 30 such that the set of the radiation source 2 and the radiationdetector 3 is rotated the plurality of turns, and

the imaging operation control means 50 controls the operation of the setof the radiation source 2 and the radiation detector 3, such that theradiation imaging operation is performed with respect to the angularposition taken by the set of the radiation source 2 and the radiationdetector 3 during the period between the state, in which the set of theradiation source 2 and the radiation detector 3 stops at the time of thepredetermined turn, and the stage, at which the velocity of the set ofthe radiation source 2 and the radiation detector 3 comes up to thepredetermined velocity at the time of the predetermined turn, theradiation imaging operation with respect to the angular position beingperformed at the time of the next turn.

With the modification described above, the problems are prevented fromoccurring in that a position, at which the radiation imaging operationis not performed, arises with respect to the period between the stage,at which the rotation of the set of the radiation source 2 and theradiation detector 3 is begun, and the stage, at which the velocity ofthe set of the radiation source 2 and the radiation detector 3 comes upto the predetermined velocity.

Also, the radiation imaging apparatus 1 in accordance with the presentinvention may be modified such that the rotation control means 40 beginsthe driving of the rotation driving unit 30 at the time, at which thebreathing signal BS represents at least 95% of the maximum inspiration,and such that the rotation control means 40 ceases the driving of therotation driving unit 30 at the time, at which the breathing signal BSrepresents a level lower than 95% of the maximum inspiration. With themodification described above, lowering of the image quality due to theup and down breathing movement is suppressed to the minimum.

The radiation imaging apparatus and the radiation imaging method inaccordance with the present invention may be embodied in various otherways. For example, FIG. 4 illustrates the cases where the rotationdriving of the rotation driving unit 30 is begun at the time, at whichthe breathing signal BS represents at least 95% of the maximuminspiration. Alternatively, since the breathing is capable of beingcontrolled artificially to a certain extent, voice outputting or displayoutputting for navigation may be performed, and the beginning or thecompletion of the rotation driving may be controlled in accordance witha specified timing and the breathing signal BS.

Also, in the embodiment described above, the radiation imaging operationis performed with the predetermined imaging operation timing under thecondition in which the set of the radiation source 2 and the radiationdetector 3 is being rotated. In cases where it is assumed that the X-rayirradiation is performed within a sufficiently short period of time withrespect to the rotational velocity (for example, within an X-rayirradiation time of 1 ms in cases where the rotational velocity is 360deg/30 sec), the motion artifact due to the rotation becomes as small asa negligible extent.

From the view point of the motion artifact, the rotation control means40 may rotate or stop the set of the radiation source 2 and theradiation detector 3 in accordance with the breathing signal BS and maycontrol the rotation driving unit 30 such that the rotation driving ofthe set of the radiation source 2 and the radiation detector 3 is ceasedat the time of the radiation imaging operation. Specifically, in suchcases, the radiation imaging operation is performed in the state inwhich the set of the radiation source 2 and the radiation detector 3stops. Also, after the radiation imaging operation has been completed,the rotation control means 40 rotates the set of the radiation source 2and the radiation detector 3 to the position for the next imagingoperation (for example, by a specified angle of 1 deg) or to theposition corresponding to the next imaging operation timing. Theoperations described above are iterated within the aforesaid rotationdriving period RP. In such cases, the lowering of the image quality dueto the motion artifact caused to occur by the rotation is prevented.

1. A radiation imaging apparatus, comprising: i) a radiation source forirradiating radiation to an object, ii) a radiation detector fordetecting the radiation carrying image information of the object at thetime at which the radiation is irradiated from the radiation source tothe object, iii) a rotation driving unit for rotating the set of theradiation source and the radiation detector around the object, iv) abreathing sensor for detecting a state of breathing of the object as abreathing signal, v) a heartbeat sensor for detecting a state ofheartbeat of the object as a heartbeat signal, vi) rotation controlmeans for controlling such that the driving of the rotation driving unitis begun at the time at which the breathing signal having been detectedby the breathing sensor has come into a predetermined state, and suchthat the driving of the rotation driving unit is ceased at the time atwhich the breathing of the object has come into a state other than thepredetermined state, and vii) imaging operation control means forcontrolling the operation of the set of the radiation source and theradiation detector, such that a radiation imaging operation is performedat the time, at which the heart has come into a predetermined state, inaccordance with the heartbeat signal having been detected by theheartbeat sensor within a rotation driving period, during which therotation driving unit performs the rotation driving by being controlledby the rotation control means.
 2. A radiation imaging apparatus asdefined in claim 1 wherein the rotation driving unit rotates the set ofthe radiation source and the radiation detector at a predeterminedvelocity, and the imaging operation control means controls the operationof the set of the radiation source and the radiation detector, such thatthe radiation imaging operation is performed after the set of theradiation source and the radiation detector has been driven for rotationfrom the state, in which the set of the radiation source and theradiation detector stops, and after the velocity of the set of theradiation source and the radiation detector has thus come up to thepredetermined velocity.
 3. A radiation imaging apparatus as defined inclaim 1 wherein the rotation control means has a function for returningthe position of the set of the radiation source and the radiationdetector in the direction, which is reverse to the direction of therotation of the set of the radiation source and the radiation detectorat the time of the radiation imaging operation, after a radiationimaging operation performed most recently has been completed or before anext radiation imaging operation is begun, such that the rotationdriving of the set of the radiation source and the radiation detector isbegun at a predetermined velocity from a predetermined position.
 4. Aradiation imaging apparatus as defined in claim 3 wherein the rotationcontrol means has the function for returning the position of the set ofthe radiation source and the radiation detector, such that the rotationdriving of the set of the radiation source and the radiation detector isbegun at the predetermined velocity from the position, at which therotation driving of the rotation driving unit has been ceased at thestage of the radiation imaging operation performed most recently.
 5. Aradiation imaging apparatus as defined in claim 2 wherein the imagingoperation control means controls such that the radiation imagingoperation is performed at the time, at which the set of the radiationsource and the radiation detector takes a predetermined angularposition, during the period between the state, in which the set of theradiation source and the radiation detector stops, and the stage, atwhich the velocity of the set of the radiation source and the radiationdetector comes up to the predetermined velocity.
 6. A radiation imagingapparatus as defined in claim 2 wherein the rotation control meanscontrols the rotation driving unit such that the set of the radiationsource and the radiation detector is rotated a plurality of turns, andthe imaging operation control means controls the operation of the set ofthe radiation source and the radiation detector, such that the radiationimaging operation is performed with respect to an angular position takenby the set of the radiation source and the radiation detector during theperiod between the state, in which the set of the radiation source andthe radiation detector stops at the time of a predetermined turn, andthe stage, at which the velocity of the set of the radiation source andthe radiation detector comes up to the predetermined velocity at thetime of the predetermined turn, the radiation imaging operation withrespect to the angular position being performed at the time of the nextturn.
 7. A radiation imaging apparatus as defined in claim 1 wherein therotation control means controls such that the rotation driving of theset of the radiation source and the radiation detector by the rotationdriving unit is ceased at the time of the radiation imaging operation,and such that the rotation driving is again begun after the radiationimaging operation has been performed.
 8. A radiation imaging apparatusas defined in claim 1 wherein the rotation control means begins thedriving of the rotation driving unit at the time, at which the breathingsignal represents at least 95% of the maximum inspiration, and such thatthe rotation control means ceases the driving of the rotation drivingunit at the time, at which the breathing signal represents a level lowerthan 95% of the maximum inspiration.
 9. A radiation imaging method,utilizing: i) a radiation source for irradiating radiation to an object,ii) a radiation detector for detecting the radiation carrying imageinformation of the object at the time at which the radiation isirradiated from the radiation source to the object, iii) a rotationdriving unit for rotating the set of the radiation source and theradiation detector around the object, iv) a breathing sensor fordetecting a state of breathing of the object as a breathing signal, andv) a heartbeat sensor for detecting a state of heartbeat of the objectas a heartbeat signal, wherein a plurality of radiation images of theobject are acquired by iterating the steps of: beginning the driving ofthe rotation driving unit at the time at which the breathing signalhaving been detected by the breathing sensor has come into apredetermined state, performing a radiation imaging operation with theset of the radiation source and the radiation detector at the time, atwhich the heart has come into a predetermined state, in accordance withthe heartbeat signal having been detected by the heartbeat sensor withina rotation driving period, during which the rotation driving unitperforms the rotation driving, and ceasing the rotation driving of therotation driving unit at the time at which the breathing of the objecthas come into a state other than the predetermined state.